Current downhole acoustic (or sonic) tools use acoustic transmitters configured to generate acoustic wave signals having certain characteristics (i.e. frequency, amplitude, direction, etc). The acoustic waves travel through the surrounding environment by means of a pressure variation of the media and are reflected towards receivers where a signal is recorded. The acoustic waves recorded by the receivers are then analysed in a process known as sonic log interpretation and acoustic images (e.g. 3D borehole images) may be generated to try to determine the nature and/or structure of the environment.
In order to accurately interpret the received acoustic waves it is necessary to extract the acoustic characteristics of the transmitters. Today it is assumed that the transmitted signal will be the same as a simulated electronic signal generated by the tool and imposed by the tool design. Some authors recognise that some source anomalies can be identified in sonic logs as amplitude variations but these cannot be quantified. Accordingly, the traditional method of extracting source signals from received signals is prone to large errors and amplitude and frequency variations cannot be quantified in a defined manner.
It is therefore an aim of the present invention to provide an acoustic measurement tool which addresses at least some of the afore-mentioned problems.